1. Field of Invention
The present invention relates to a spring leaf and an overrunning clutch provided with the same.
2. Related Art
An overrunning clutch is a clutch that automatically engages or disengages when the relative moving speed of a driving part and a follower part changes or the reciprocation direction changes; and is a basic component in the mechanical transmission of Mechanical & Electrical Integration. The major functions of the overrunning clutch are backstopping, accurate positioning, torque transmission, or breaking the torque, so the overrunning clutch is also referred to as a backstop or one-way bearing, which is widely applied in the machine tools, packaging machines, printing machines, light industry machines, textile machines, petrochemical machines, cement machines, metallurgical machines, transportation machines, reducers, and the like. The overrunning clutch has a great varieties, among which the ratchet overrunning clutch, needle roller overrunning clutch, and sprag overrunning clutch are the most commonly used. The structure of the needle roller overrunning clutch includes an inner ring, an outer ring, a needle roller, and a spring. The needle roller keeps the overrunning clutch at a ready to work state depending on the elasticity of the spring, and the spring provides a buffer effect for the needle roller, thereby ensuring sustained stable running of the overrunning clutch. Therefore, the shape and structure of the spring and the installation and fixing manner thereof exert great impact on the performance index such as the sustained running stability and using lifespan of the clutch, and thus the spring is a critical part of the overrunning clutch. The spring is required to maintain the sustained elastic restoring force and meanwhile provide a good anti-fatigue performance, and is reliably positioned and fixed in the overrunning clutch. Therefore, the overrunning clutch manufacturers are devoted themselves to the research of the spring structure of the overrunning clutch and the installation and fixing manners thereof. For example, Chinese Patent No. CN2206861Y discloses a “Double Needle Roller One-way Break Clutch”, in which the spring of the double needle roller one-way break clutch is an oval spring leaf, and is placed in the slot of the needle roller hole in the needle roller stand, for pressing the needle roller. The needle roller stand of the structure is difficult to manufacture. As the spring leaf is only placed in the raised slot of the needle roller hole in the needle roller stand, under the condition of a high rotational speed, there is a risk of detachment displacement failure of the spring leaf. Chinese Patent No. CN2252910Y discloses a “Sealed One-way Stop Assembled Clutch”, in which the spring of the sealed one-way stop assembled clutch is an S-shaped flat spring. Likewise, this structure has the deficiency that the retainer is difficult to fabricate. U.S. Pat. No. 6,170,626 discloses an overrunning clutch, in which the spring structure is a spring leaf with arc-shaped front ends for supporting the needle roller, and back ends of the spring leaf form an elastic clamp, for buckling the spring on the crossbeam of the retainer. This spring structure can improve the bearing capability of the spring to some extent, but the elastic clamp at the back end buckles the spring on the crossbeam of the retainer, so that when the rotational speed is high, there is a risk that the elastic clamp may be disengaged from the crossbeam of the retainer under the centrifugal force. The tail end of the arc spring leaf is formed by punching, and the end surface of the tail end after being bent is in contact with a supported roller at an acute angle, which in use, may easily cause the abrasion of the partial surface of the needle roller and generate noises. Meanwhile, the tail end of the arc spring leaf may also be easily abraded, which causes insufficient elasticity supported on the needle roller and loses the function of the overrunning clutch. Japanese Patent No. JP2006-226318A also discloses some spring leaf structures used in the overrunning clutch. However, the part of the spring leaves for supporting the needle roller in suspension is foldable. After a force is applied on the spring leaves, the folded root may be easily broken. Besides, the potential displacement and detachment of the spring leaf exist during the reciprocation of the clutch at a high rotational speed and high frequency. For example, referring to FIGS. 8, 9, and 10, as the spring leaf is suspended on the crossbeam of the retainer, the spring leaf and the retainer may generate a certain displacement in the axial direction, so the elasticity of the spring leaf received by the needle roller in movement is unstable. Moreover, during the reciprocation of the clutch at a high rotational speed and high frequency, the spring leaf is impacted by the needle roller, which easily causes the displacement and detachment. In addition, the part of the spring leaf that supports the needle roller in suspension is a bending part formed by punching, and when the spring leaf is under a force in operation, the folded root may be easily broken, resulting in a defective product. Further, as shown in FIGS. 3, 4, 5, 6, 7, and 12b, the contact position of the spring leaf and the needle roller is located at the middle part of the needle roller instead of being close to the end part, so the force received by the needle roller in movement is uneven, which may easily cause tilting of the needle roller.